In the development of internal combustion type engines, the practice of controlling the charge and the subsequent ignition thereof, has afforded a highly efficient engine. Further, and toward minimizing the amount of harmful pollutants discharged into the atmosphere, means and systems have been provided to regulate both the exhaust gas quality as well as the condition of the intake flow.
One such engine adapted to operate in this improved manner, incorporates a system as disclosed in U.S. Pat. No. 2,484,009, issued in the name of Barber, and dated Oct. 11, 1949. Briefly the basic concept of this system and means of engine operation, resides in the close control of the fuel flow and the combustion supporting gas introduced to the engine, as well as the firing event. More specifically, said system provides that an internal combustion engine be so equipped to operate on a stratified charge which is periodically formed in an engine combustion chamber.
Thus, a combustion supporting gaseous medium such as air, or a modified mixture thereof, is introduced to an engine cylinder or combustion chamber. Said air charge is urged into the cylinder in such manner to assume a rapidly swirling path adjacent to the cylinder walls. The swirling combustion supporting stream is thereafter in the usual manner, compressed by an advancing piston head until the latter reaches top dead center position.
Immediately prior to said top dead center position, a predetermined volume of liquid fuel is forcibly injected into the cylinder by means of one or more injector nozzles. The injection is so controlled and directed as to form a liquid patch of limited area. A portion of the fringe of said patch, by virtue of its mixing with air, comprises a combustible medium or atmosphere. The latter occurs as a result of the peripheral mixing of the fuel patch moving at a high rate of speed with the combustion supporting gas.
The engine fuel injector nozzle as well as the igniter, are so arranged within the combustion chamber that the fuel patch will be ignited at a point closely adjacent to the igniter. Consequently, upon ignition the fuel patch will progressively mix with the combustion supporting gas until the patch is eventually consumed. At the termination of the resulting power stroke, exhaust gases are forced from the engine in the usual manner by way of an exhaust valve.
In the noted form of engine, control thereof in response to loading is achieved by varying the rate of fuel injection. Thus, normally with increased load, the intake volume of air per stroke is relatively constant, while the rate of fuel intake increases.
Inherently, this type of engine system embodies a number of advantages over the normal internal combustion engine which operates basically on an Otto cycle, using a relatively constant fuel/air ratio in the premixed charge. More specifically, the present engine as operated on a stratified charge, will provide not only a higher efficiency, but is capable of operating satisfactorily on varying grades of fuel with respect to both octane and cetane numbers.
One detriment however found to be present due to the nature of the air and fuel injection, results from an inherent characteristic of the engine and combustion system. For example, for virtually all engine operating conditions, there will be a varying fuel/air ratio of charge which is introduced into the combustion chamber. Thus, at relatively low loads the amount of fuel injected will lean the combustible charge defined by the mixture of said fuel with previously drawn-in air or combustion supporting gas. This leanness of the charge results in the engine running relatively cold such that the exhaust gases will contain a considerable amount of undesirable air polluting materials when such gases are discharged directly into the atmosphere. Further, reaction of said "cold" gases with a catalytic filter or the like will be minimized or dampened since the catalyst will be caused to operate at a lower temperature.
Toward overcoming these inherent disadvantages in the operation of an internal combustion engine there is presently provided a method of operating such an engine, as well as the apparatus therefor. In accordance with the disclosed method, a stratified charge including discrete injections of air and fuel, are separately introduced to the engine combustion chamber. The air is rapidly rotated within the chamber as the piston head advances toward the top position on the compression stroke.
Prior to the cylinder reaching the top dead center position a pressurized fuel stream is introduced to the combustion chamber to form a limited area patch of fuel in the circulating air. The fringes of the fuel patch contact the rapidly moving swirling air to form said fringe areas into a combustible mixture. The latter is then ignited by the ignition means to initiate the power stroke.
At low loads the overall fuel mixture charge is in effect enriched through the step of throttling the air stream. Ignition of the combustible mixture is thereby more readily facilitated such that the latter burns at a higher temperature and thus minimize undesirable emissions in the exhaust stream.
Thereafter as engine load is progressively increased, the throttling step is progressively reduced until at optimum conditions of load, throttling is completely discontinued.